Paperboard, generally in thicknesses of 0.010 to 0.042 inch (0.25 to 1.07 millimeter), is widely utilized in the manufacture of small folding paper cartons, phonograph record jackets, blister pack packaging cards, and the like. The paperboard is supplied in continuous rolls which must be cut to the proper length and width for each application. This cutting leaves the edges coarse and covered with particles from the paperboard's clay coating.
These particles are often as large as 1/8 inch (3.2 millimeters) across. They cling to the cut edge of the paperboard and may be held in place by paper fibers. The particles may later come loose and find their way to either surface of the paperboard where they cause problems when an attempt is made to print upon that surface of the paperboard.
Particles as small as 1.38 thousandths of an inch (35 microns) must not be allowed to remain upon the surfaces of the paperboard which are to be printed upon. A particle of this size which finds its way to the print blanket of an offset printing press can cause a blemish upon the printed surface of the paperboard which is 1.97 thousandths of an inch (50 microns) wide. Since the human eye can detect blemishes as small as 1.97 thousandths of an inch (50 microns), particles down to this size must be removed prior to printing upon the surface of the paperboard.
Particles smaller than 1.38 thousandths of an inch (35 microns) are less important, but still significant. These are the most numerous particles and are the first to collect on the print blanket, giving it a hazy appearance even though the individual particles are invisible to the eye. The accretion of fine particles on the print blanket can cause non-uniformity in the printing of large color fields. Further, an agglomeration of fine particles can grow large enough to cause visible blemishes. It is desirable to limit the accretion of fine particles on the print blanket by removing them from the surface of the paperboard.
Conventional vacuums, vacuum brushes, and air-knives provide very little cleaning in the range below 2.76 thousandths of an inch (70 microns).
A prior art search did not disclose any patents for devices which treat the edges of paperboard in the manner of the present invention. The following patent documents were considered in the investigation and evaluation of the prior are relative to this invention.
______________________________________ PATENT NUMBER INVENTOR ISSUE DATE ______________________________________ 1,591,167 (Britain) Bleasdale 17 June 1981 4,129,919 (U.S.) Fitch et al 19 Dec. 1978 3,117,333 (U.S.) Murray et al 14 Jan. 1964 ______________________________________
The Bleasdale patent discloses an apparatus for removing the photographic emulsion from microfilm. It is concerned with treating the upper and lower surfaces of the microfilm and not the edges.
The Murray patent discloses an apparatus which uses rotating brushes to remove dust from microfilm frames mounted in data storage cards. This device only cleans the upper and lower surfaces of the microfilm.
The Fitch patent discloses an apparatus for scrubbing and drying the upper and lower surfaces of printed circuit boards.
The above mentioned devices are directly concerned with treating the upper and lower surfaces of their respective working materials, whereas the present invention buffs and cleans all four of the edges of its working material as well as the upper and lower surfaces where required.